Stress and/or accumulated damage monitoring system

ABSTRACT

A monitoring system implemented on a truck. The system includes: a plurality of strain and pressure gauges at critical locations at which a failure is predicted to occur; a processor with memory hardware configured to process the acquired real-time data from the gauges to determine measures of actual instantaneous stress and a real-time operating state; an output device configured to provide information comparing measures of actual instantaneous stress with corresponding reference values of maximum allowable stress, and to provide the real-time information derived from the real-time operating state. The real-time information derived from the real-time operating state preferably includes an amount of cumulative damage or closeness to failure having regard to the measures of actual instantaneous stress and the real-time operating state.

FIELD

The present invention relates to earthmoving equipment, in particular toa real-time stress and/or accumulated damage monitoring system.

BACKGROUND TO THE INVENTION

In the mining industry there is a continual effort to lower the cost ofextraction of ore or overburden. A competition in the cost calculationexists between operating earth or ore extraction equipment at a maximumcapacity and the damage caused to the equipment by overloading orfatigue. Manufacturers of mining equipment typically seek to protectthemselves from liability for equipment failure by specifyingconservative operating conditions that attempt to keep the failure ratevery low, whereas the interest of the mine operator is to find the mosteconomical balance between ore extraction and damage that minimizes thecost per tonne of ore extraction.

Manufacturers and third party providers provide a range of monitoringsystems to provide information on loads and relative stressesexperienced by draglines, utilizing strain gauges on certainrepresentative structural components. Using such systems it is possibleto record a time profile of the strain measured at the strain gauges andthereby provide reports on how the strain varies from one time periodrelative to another, enabling relative comparisons to be made betweendifferent operators and operating conditions and information on whichtime period produced relatively more stress/damage at the measuredlocations compared to another. While useful, such relative informationcannot advise on how close the equipment is to failure or how muchdamage is occurring through fatigue. Without such information, themonitoring system is of limited use in assisting the mine operation andequipment operator in their goal in cost-efficiently maximizingproduction while minimizing damage to the equipment.

According to the current state of public knowledge in the art,monitoring systems that can usefully advise in real-time on whether thestructure is operating within the design limits, the actual closeness tofailure or the actual rate of cumulative damage, is not available. Thecurrent systems provide a relative measure which could lead toinaccuracies that could result in frequent false alarms and warnings.

There is therefore a need to provide an improved monitoring system thatcan provide such information.

Through an accumulation of long standing experience and research, theinventor has realized that enabled by careful observation and structuralanalysis as described herein guiding the placement, calibration andinterpretation of strain gauges, a monitoring system can be providedthat can surprisingly provide such reliable direct advice, in real-timeto an operator and to mine management.

SUMMARY OF THE INVENTION

According to a broad aspect of the invention there is provided a stressand/or accumulated damage monitoring system for earth moving equipment.The system includes strain gauges that measure strain at locations onearth moving equipment. The earth moving equipment is one of anexcavator, a truck, a shovel, a drill, a wheel loader, and a grader.

The system further includes a data acquisition unit to acquire real-timestrain data from the strain gauges and a processor and memory to processthe acquired real-time strain data. This data is used calculate one ormore measures of actual accumulated damage and/or actual instantaneousstress.

The system further includes an output device to provide informationcomparing the measures with corresponding reference values.

In the embodiment configured for an excavator, the system uses at leastone of the strain gauge locations on a boom or stick of the excavator.The strain gauges on the boom and stick are preferably used toaccurately estimate the stress or cumulative damage that the boom andstick experience during a range of operating modes. Preferably thesestrain gauge locations are those determined to be the most vulnerable tofailure during operation and those most useful for predicting failure orcumulative damage in another part of the boom or stick. Preferably, atleast one of the output devices is a display in a driver's cabin of theexcavator.

Preferably, at least one of the output devices is equipped to wirelesslytransfer data to a manager's office or other remote locations to enablethe information derived from the measures and the operating state to beused in maintenance planning, operator training, mining planning and/orother management tasks. Information comparing the measure of accumulateddamage with its corresponding reference values may be expressed by atleast one of the output devices so as to advise or trigger the requiredlevel of inspections of the boom, stick and the main frame.

Preferably, the accumulated damage is used to define or adjust thereference values associated with the strain gauge locations to reduceunscheduled stoppages.

The system may include at least one load, position or orientation gaugefor gauging the force applied by an actuator or its position ororientation. Thus, the data acquisition unit in the system preferablyacquires real-time load, position or orientation data from the loadposition or orientation of one or more of the gauges.

The processor and memory used in the system processes the acquiredreal-time load, position or orientation data to determine an operatingstate of the equipment. At least one of the output devices also providesinformation derived from the operating state. Where the system isadapted for an excavator, at least one of the strain gauge locations maybe disposed on a boom or stick of the excavator and the operating statemay include information on the position of the boom and stick. Theinformation derived from the operating state may include programmedadvice regarding how to reduce one of the measures of instantaneousstress or accumulated damage. Raw data may be recorded and analyzed toclearly identify a root cause for an incident of extreme high stress ordamage.

In various embodiments, the information comparing the measures withcorresponding reference values is presented as the measures ofinstantaneous stress or accumulated damage normalized with respect tothe reference values; the reference value for stress is a maximumallowable stress; the reference value for accumulated damage is acalculated from a predefined target fatigue rate; the measures ofaccumulated damage are compared with the reference values by expressingthem as implied lifetimes or maintenance intervals; and an alarm isactivated on at least one of the output devices when one of the measuresof instantaneous stress exceeds or approaches the associated referencevalue.

The system may be configured for a truck wherein at least one of thestrain gauge locations is disposed on a chassis of the truck. An alarmmay be activated on at least one of the output devices when one of themeasures of instantaneous stress exceeds or approaches the associatedreference value. The alarm may comprise feedback to a driver of thetruck advising the driver to reduce speed by a specified amount if aselected one or more of the threshold limits is exceeded when hauling.

The system may be configured for a drill having a pivotable mast. Thestrain gauge locations are then, preferably, one or more locationscritical for detecting when an operator is attempting to raise the mastwith a mast locating pin still engaged, or is toggling hoist cylindersof the mast to disengage a stuck locating pin.

The system may be configured for an hydraulic shovel.

The system may be configured for an electric rope shovel having a boomand dipper handle. For this embodiment, the strain gauge locationspreferably include one or more locations on the boom. The strain gaugelocations on the boom may comprise one or more locations that can beused to infer lateral bending stresses occurring in the dipper handle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an excavator to which an embodiment of theinvention has been applied and is described herein;

FIG. 2 is a block diagram of an embodiment of the invention;

FIG. 3 is a diagram of a side view of the boom and stick of a HitachiEX3600 excavator showing sensor locations.

FIG. 4 is a screen display arrangement for an excavator in theembodiment described.

FIGS. 5a and 5b are views of the chassis of a Caterpillar CAT793 C or Dtruck to which another embodiment of the invention has been applied,showing regions where failures can occur.

FIGS. 5c and 5d are views of the CAT793 C or D truck chassis of FIGS. 5aand 5d , showing sensor locations for the embodiment.

FIGS. 6a and 6b are views of the chassis of a Caterpillar CAT797 B or Ctruck to which yet another embodiment of the invention has been applied,showing regions where failures can occur.

FIGS. 6c and 6d are views of the CAT797 B or C truck chassis of FIGS. 6aand 6d , showing sensor locations for the embodiment.

FIGS. 7a and 7b are perspective views showing sensor locations fromdifferent sides of the boom of an electric rope shovel, near the shippershaft; and FIG. 7c is a view from the underside of the boom of theshovel showing further sensor locations.

FIG. 8 is a view of interior components of the boom of FIGS. 7a, 7b and7c , showing sensor locations for inferring dipper handle stresses dueto lateral bending;

FIG. 9 is a part view of a drill, near the pivot point of the mast.

DETAILED DESCRIPTION OF EMBODIMENTS

Non-limiting embodiments of the current invention will now be described.

EXAMPLE 1 Hitachi EX3600 Excavator

Referring first to FIG. 1, the embodiment to be described is applied toan Hitachi EX3600 excavator 1 comprising bucket 10, stick 11 and boom12. Boom 12 is rotatably attached to the excavator body and is driven byhydraulic piston actuator 15. Stick 11 is rotatably attached to boom 12and is driven by hydraulic piston actuator 14. Similarly, bucket 10 isrotatably attached to stick 11 and is driven by hydraulic pistonactuator 13. Excavator body has driver's cabin 21 atop engine room 22.

Referring also now to FIGS. 2 and 3, a plurality of sensors 30 aredistributed over boom and stick, including piezoelectric strain gauges,pressure sensors and inclinometers. The strain gauges 52-60 are locatedat strain gauge locations determined by detailed analysis (described inmore detail later) as the most critical locations on the boom and stickthat can be used to accurately estimate the stress or cumulative damagethat the boom and stick experiences during a range of operating modes.

In making best use of the invention, considerable care is taken indeciding these locations, as the extent to which they are accurate has alarge bearing on the usefulness of the absolute measures of accumulatedfatigue and/or instantaneous stress that are reported in real-time bythe system for optimizing the operation of the excavator. In FIG. 3,showing the critical locations identified by the inventor for theHitachi EX3600, pairs of strain gauge locations, on the left or rightside in the third dimension, are shown by short black lines. Forexample, strain gauges 51 and 52 are located where shown on the bottomplate, close to the left and right edge of the boom respectively. Bycontrast, strain gauges 53 and 54 are located where shown on top leftand right side plates of the boom. Locations 51 to 54 are useful becausethey are predicted by detailed analysis and observed in the field to bepoints of maximum stress and failure cracks in common operating modes.The strain gauge locations are useful to be provided in pairs such as 51and 52 on the left and right sides respectively, as differentialreadings between the individuals of a pair together with the straingauges 55-58 detects a twisting torque or lateral bending, which can beused to advise an operator of uneven loading or impact, or side loading,or to further predict closeness to failure at other unmeasuredlocations. Locations 55-58 are useful because detailed analysis showsthat these locations, while not likely to fail, are critical inpredicting the stress state of the boom and stick at other locationsthat could fail due to specific loading scenarios. Locations 59 and 60are useful in predicting the stress state in the stick in combinationwith locations 55-58.

It will be appreciated that locations will vary each time themanufacturer modifies its models, and detailed analysis to confirm thecorrect locations is required to be performed for each model variation.

Referring again to FIG. 2, sensor wire bundle 36 passes to computingequipment comprising data acquisition unit 41, processor and memory 42and wireless communications controller 43. The computing equipment iscomposed of standard off the shelf systems and/or a custom designedsingle board system, conveniently located in engine room 22 and suppliedwith electrical power from the excavator system, but also containingrechargeable lithium battery power supply to prevent excessive restartssuch as after the excavator is switched off during a shift. Input/Outputdevice 37 in the form of touch screen is located for the use of thedriver in cabin 21 or will utilize a 3rd party screen which is availablein the cabin 21. Output and remote programming control is also providedby wireless communications controller 43 which links to wireless minedata network 45, enabling remote data communication with mine management46.

Sensors 30 produce voltage signals which are transmitted as currentsignals over current loop circuits 32, conveniently terminating at acommon point 32 on the hydraulic manifold.

Pressure Sensors

The pressure sensors which in this embodiment measure the force in thehydraulic circuits are most easily placed near the manifold where thehydraulic lines meet. Pressure sensors on the hydraulic lines areusually already supplied on the excavator when manufactured, and mayalternatively be accessed. The pressure data is used to monitor theextensive and retractive forces applied to bucket, stick, boom, theforce urging rotation of the body and the forwards/backwards force onthe tracks. The net forces applied on the boom, stick and bucket andswing right or left are calculated as follows:Net Force=(Extension Pressure−Retraction Pressure)×Strut bore area.Net Swing Force=(Swing Right−Swing Left)×Strut bore area.

The measurement range for pressure transducers are ±10,000 psi.

Inclinometers

Inclinometer 71 measures the angle of inclination of boom 12, andinclinometer 72 measures angle of inclination of stick 11. A furtherinclinometer 73 may be positioned on the bucket 10 (bucket not shown inFIG. 3) to measure the angle of inclination of bucket 10, although thisparameter is of less relevance.

Specification of Strain Gauges, Fitting and Processing

The measurement range for the strain gauges is around ±500 MPa (±2500μs) with signal conditioning units have a dynamic range of ±1000 MPa(±5000 μs) and contains anti-aliasing filters and digital filtersaccurately measure up to a frequency range of 200 Hz with 16 bitresolution. The channel configuration defining the sensor location,type, and calibration factors to be used are specified and stored in adatabase and configuration files. Since the strain gauges are to be usedto compute absolute measures of stress, care is taken carefully toinstall them with the appropriate waterproofing to minimize signaldegradation. Drift is also automatically detected and the systembalanced and calibration parameters updated regularly—drift in a straingauge can be detected by calibrating strain to zero when the excavatoris in an idle state with bucket resting on the ground in a specificconfiguration. Drift of sensors will affect the strength criteria as itwill introduce an apparent additional strain (additional) to the dynamicstrain measurement. The drift of sensors does not affect the rainflowanalysis of cumulative damage calculations.

Integration of Sensor Readings to Derive Information

Using the inclinometer readings, the instantaneous position of the boomand stick is calculated by trigonometry, and together with the hydraulicpressure sensor readings a full real-time picture of an operating stateof the excavator may be deduced by the system. An important operatingstate of high stress at certain of the strain gauge locations typicallyensues when the boom and stick are fully outstretched, as detected bythe inclinometers. A coincidence of high measured stress at one of thesecertain strain gauges and a measured fully outstretched operating stateenables the processor to provide the operator with real-time informationderived from the operating state, such as a warning and an appropriatecorrective action to allow continued excavation without alarm andreduced cumulative damage with minimal or no impact on the mine plan.The appropriate corrective action might be for example, that during adouble benching operation that is resulting in damage and stress outsidedesign limits, the driver is advised to change the operatingconfiguration by moving the excavator closer to the face and changingforces applied by the operator to the boom and stick actuators 13 and14. Processor and memory 42 is programmed to respond to a range of suchtypical situations and to provide the appropriate real-time advice, inaddition to providing simple high stress and/or accumulated fatiguealarms.

Data Acquisition and Calibration

Current loop sensor wires 36 terminate at multi-channel data acquisitionunit 41 which is programmed to take samples at 20 times per second (upto 200 Hz may be useful). Raw data is used by the processor to calculateabsolute measures of stress and accumulated fatigue, using a range ofcalibration constants, some predetermined based on the fatigue categorydetail, dead weight of the system at predefined configurations and someupdated by regular calibration as required by the system software. Rawdata is kept also to provide a “black box” resource to analyze orinvestigate any incident or when a failure occurs. The raw data can bereplayed to clearly identify the root cause for incident of extreme highstress or damage as the combination of the all sensors can define thestate of excavator operation at any instant.

Measurement of Instantaneous Stress and Comparison with Reference Values

As described above, the strain gauges are well protected from waterdamage and are regularly corrected for drift. The actual stress at ameasurement location is calculated by multiplying the measured strain byYoung's modulus for the thickness and grade of metal (usually steel) atthe measurement location. This information is obtained from themanufacturer if available, or determined by direct measurement of thecomponents if not obtainable from the manufacturer.

A reference value of maximum allowable tensile or compressive stress (or“strength”) associated with the strain gauge location can be calculated,from a stress at which the equipment is predicted to fail, either at thestrain gauge location itself (for locations such as 51-54) or at othernon-measured locations predicted to be most vulnerable based on a FEAanalysis, multiplied by a safety factor.

The processor calculates for data presentation purposes normalizedcompressive and tensile stresses as a ratio or percentage of themeasured stress to the maximum allowable stress taking into account thedead load stress for the particular location at the set configurationusing FEA when the system is calibrated.

Calculation of Cumulative Fatigue and Comparison with Reference Values

Rainflow analysis, the commonly accepted method of fatigue analysis, iscarried out utilizing the data from each strain gauge to estimatecumulative damage and fatigue life. Digital filtering to cut off stresscycles (extension followed by contraction) lower than a pre-set value(e.g 2 MPa) is utilized to filter the data. The start and end of adigging cycle (dig, swing, dump and return) is determined by monitoringhydraulic pressure sensors and/or the inclinometer, and cumulativefatigue over the digging cycle is calculated. The cumulative damage percycle or for a specific time period and the estimated fatigue life ofthe component (assuming that the excavator would operate continuouslywith a similar load cycle) is displayed to the operator and stored inthe memory for use by maintenance personnel and engineers. The system isalso integrated with some 3rd party suppliers of fleet managementsystems to provide cumulative damage per truck load cycle. The followingequation is utilized to calculate cumulative damage (D):D=KΣn _(i)σ_(i) ^(m)wheren_(i) is the number of stress cycles with a (digitally filtered) stressrange of σ_(i)K=damage factorm=damage power.

The values of K and m are typically prescribed by engineering standards(m is typically 3) but may be varied by actual experience where thephysical situation does not match the underlying assumptions.

The estimated damage per digging cycle is reported as damage per hour.D _(hr)=3600(D/t)

The Life (L) in service hours, of the particular location can be definedas:L=1/D _(hr)

The estimate fatigue is normalized for presentation as follows:Normalized fatigue=Fatigue Life limit in service hours(LL)/L

The reference values of threshold limits (LL) for fatigue life arecustomized for each critical location, based on the needs of thecustomer (Productivity VS Machine component Life expectation). If thenormalized fatigue exceeds 100%, this indicates that the fatigue isfaster than planned and an alarm/warning is provided to the driver andthe number of sensors that exceed the limit is recorded in summaryinformation.

The accumulated damage may be used to define a trigger for inspection ofthe specific components such as the boom, stick so that any cracksinitiating can be detected at an early stage prior to cracks reachingcritical size which will force unscheduled stoppages. For example whenthe accumulated damage reaches a certain preset values the system willtrigger an alarm to the operations to conduct an inspection of the boomat specific locations. The alarm is based on estimation on growth ratebased on a pre-existing crack of a very small size. If a crack detectedat an early stage, the machine could be operated safely for some timeuntil repairs are scheduled with cumulative damage monitored anddisplayed to operations in real-time.

Display of Normalized Measures

A typical display 70 on the cabin computer screen 37 output device isshown in FIG. 4. This display may be a standalone screen but may also beintegrated with a display system of a third party supplier or themanufacturer, where other information is displayed in a central region71.

Panel 72 shows a range of operator touch screen buttons such as to enterthe operator's ID, a delay code (why the excavator is stopped), a digmode intended by the operator. Alternatively, this information can beobtained from a third party via Ethernet, comms or TCP/IP. The sensorcalibration can be performed via the touch screen. At the bottom of thescreen a range of bars show measured absolute values normalized asdescribed above. Panel 74 shows the normalized instantaneous stress ateach sensor, and panel 75 shows the accumulated fatigue, typically overprevious digging cycle, which is estimated by the software. Payload (theweight in the bucket) can also be calculated by various methods.Whenever a normalized value approaches 100%, warning-colored stripes 83are shown and an alarm may sound. The maximum stress for the diggingsession and the maximum accumulated damage for the shift are also shownby dotted lines.

Identification of Strain Gauge Locations

The best use of invention relies on most accurate identification of thestrain gauge locations, since if inappropriate, the stress andcumulative damage figures will not be comparable with a meaningfullimit. The strain gauge locations should comprise the most criticallocations on the boom and stick that can be used to accurately estimatethe stress or cumulative damage that the boom and stick experiencesduring a range of operating modes. For the excavator of this embodiment,the modes include jocking, double benching, hard cap removal, bending ortwisting.

These most critical locations are required to reliably determine theoperating condition any time during the cycle and can vary for each typeof excavator which has to be determined by detailed analysis on a caseby case basis.

Computer structural modelling is an important tool in determining thebest strain gauge locations. A 3-dimensional digital model of the boom,stick and bucket is developed by direct measurement of each component,including its material type and thickness or the manufacturer supplieddrawings and welding parameters. The model is then subjected to finiteelement analysis (FEA) of the range of operating states in which theexcavator is used, such as double benching, jocking, twisting/bending,below ground digging etc., for a range of positions and degrees ofextension of the boom and stick. The loading conditions used for theanalysis are derived by extensive measurements conducted on severalexcavators in various mine sites. As a result of these analyses, severalcritical locations are then identified typically as regions of sensitivelocations on the boom and stick that can accurately measure the strainrequired to estimate the stress/cumulative damage the boom and sticksees during the operation. Some of the strain gauge locations will bemore critical for strength, whereas others will be more critical forfatigue. Also, some of the strain gauge locations will be points ofactual predicted failure, others will be points where measurement besthelps predict undesirable stress or fatigue at another unmeasuredlocation. The provision of strain gauges on both the left and right sideof the boom and stick is highly relevant to operating states that imparta twisting or bending, typically caused by uneven loading or forces onthe bucket, which result in large differences in the stress between leftand right sensors.

Operating experience of actual failures observed in the field aresimulated utilizing the FEA models created to confirm its accuracy. Theoperating experience is also used to directly define some strain gaugelocations. The FEA analysis will help precisely identify the location atwhich to best place the strain gauge, which typically is best placedwith a tolerance of 50-100 mm.

EXAMPLE 2 Trucks

Two embodiments applicable to a CATERPILLAR CAT793 C or D 240 tonnetruck and a CAT 797 B or C 360 tonne truck will now be describedtogether.

With currently available truck fatigue systems, the fatigue Life isbased on measurements of all criteria (Racking+Pitching+Rolling) asmeasured from strut pressures, and producing a fatigue life predictionfor the entire chassis, not for specific areas. In reality, the fatiguelife will vary significantly from location to location, depending on thestress range, number stress cycles experienced and the fatigue categorydetail of the welded connection. The various locations on the chassiswill also experience more or less damage due to the specific operatingconditions such as rack, pitch, roll and bounce. Having one curveapplied to all locations of the chassis can be extremely conservative orin some cases would be non-conservative.

Referring now to FIGS. 5a and 5b , a chassis of the CAT 793 C or D truckis shown in two perspective views. Upper superstructure 100, Main railvertical weld 107, tail casting to main rail welds 108, and torque tubeto main rail weld 109 are all areas where cracking has commonly beenobserved. In addition, the following areas are also in risk of failure(lower risk of failure): support fore 101, rear cross beam 102, mainrails 103, torque tube 104, rear cross tube 105, tail castings 106,front cross beam 110, bumper 111, front side rails 112, steering support113, front strut support 114, hoist support 115, rear suspensionsupports 116 and pin bore for rod control 117.

Referring now to FIGS. 5c and 5d , the chassis of the CAT 793 C or Dtruck is shown with strain gauge locations 151 to 162.

Referring now to FIGS. 6a and 6b , a chassis of the CAT 797 B or C truckis shown in two perspective views. Front cross beam 260, main railcasting weld 261, main rail to tail casting weld 263 and uppersuperstructure 264 are all areas where cracking has commonly beenobserved. In addition, the following areas are also in risk of failure(lower risk): front strut support 265, hoist supports 269, steeringsupport 268, front side rails 267, bumper 266, support fore 270, rearcross beam 279, main rails 278, rear cross tube 277, rear suspensionsupport 276, tail casting 275, torque tube 273, support rear 272, andcasting weld 271 and links not shown in figure.

Referring now to FIGS. 6c and 6d , the chassis of the CAT 797 B or Ctruck is shown with strain gauge locations 300 to 313. There are anadditional two strain gauges on the links (not shown).

Strain Gauge Locations

The strain gauges are placed at locations as referred to above for thetwo sample truck models, determined by detailed FE analysis utilizingthe wheel strut pressures, speed and accelerations/decelerationsmonitored during extensive testing that can be used to accuratelyestimate the stress and/or cumulative damage that the truck chassisexperiences during a range of operating modes (racking, pitching,rolling, bouncing and loading/unloading. These most critical locationsare required to reliably determine the high damage that the chassis seesduring its travel from loading (symmetrical/unsymmetrical loading) todumping and under the changing haul road conditions (driving off thepits, haul road, turning in the haul road, uneven in the haul road,driving into dump) and can vary for each type of truck which has to bedetermined by detailed analysis on a case by case basis. Computerstructural modelling is an important tool in determining the best straingauge locations. A 3-dimensional FE model of the chassis is developed bydirect measurement of each component, including its material type andthickness or the manufacturer supplied drawings and welding parameters.The model is then subjected to finite element analysis (FEA) of therange of operating states in which the truck chassis sees during itstravel, such as racking, rolling and/or pitching, under the differenthaul road conditions and loading and unloading. The loading conditionsused for the analysis are derived by extensive measurements conducted onseveral trucks in various mine sites. As a result of these analyses,several critical locations are then identified typically as regions ofsensitive locations on the chassis that can accurately measure thestrain required to estimate the stress/cumulative damage the chassissees during the operation. Some of the strain gauge locations will bemore critical for strength, whereas others will be more critical forfatigue. However in trucks fatigue is the dominant factor. The criticalsensor locations vary based on the chassis design.

Some of the strain gauge locations will be points close to the actualpredicted failure point, others will be points where measurement besthelps predict undesirable stress or fatigue at another unmeasuredlocation. For example for the Cat 793C or 793D chassis the provision ofstrain gauges at specific locations such as the torque tube to main railconnection 109 is a point of failure and is significantly influenced byracking, whereas the superstructure beam (100) is more affected bypitching. For the 797 chassis main rail casting welds 302, 304, 305, 313the cumulative damage is significantly influenced by racking andpitching. Sensors can be introduced in the tray main rail to identifytail sweeping when unloading for both truck models.

Operating experience of actual failures observed in the field issimulated utilizing the FE models created to confirm its accuracy. Theoperating experience is also used to directly define some strain gaugelocations. The FE analysis will help precisely identify the location atwhich to best place the strain gauge, which typically is best placedwith a tolerance of 30-50 mm.

Wheel Strut Pressure and Lift Cylinder Pressures

The wheel strut pressures provide the support forces given by the wheelsand primary assessment at operating states of racking, rolling, andpitching of the chassis. A change in strut pressures when stationary isused to determine a loading operating state, as it is done currently bythe manufacturer. The lift cylinder pressures are used to determine theoperating states of the start and end of unloading.

Specification of Strain Gauges, Fitting and Processing:

Analogous to the description above in relation to the excavatorembodiment, the strain gauges are fitted at locations which are mostsensitive the various modes—loading/unloading, racking, pitching, androlling. The measurement range for the strain gauges is around .+−.500MPa (.+−.2500 μs) with signal conditioning units have a dynamic range of±1000 MPa (.+−.5000 .μs) and contains anti-aliasing filters and digitalfilters accurately measure up to a frequency range of 500 Hz with 16 bitresolution. The channel configuration defining the sensor location,type, and calibration factors to be used are specified and are stored inconfiguration files. Since the strain gauges are to be used to computeabsolute measures of stress, care is taken to install them with theappropriate waterproofing to minimize signal degradation. Drift is alsoautomatically detected and the system balanced and calibrationparameters updated regularly—drift in a strain gauge can be detected bycalibrating strain to zero when the truck is stationary on level groundwith no load. Drift of sensors will affect the strength criteria as itwill introduce an apparent additional strain (additional) to the dynamicstrain measurement. The drift of sensors does not affect the rainflowanalysis of cumulative damage calculations.

Load Gauges

The system comprises load gauges to help identify operating states. TheWheel strut pressures are combined in the following manner to determinethe operating states of racking, pitching and rolling.Racking=PFR+PRL−(PFL+PRR)Pitching=PFR+PFL−(PRR+PRL)Rolling=PFR+PRR−(PFL+PRL)wherePFR=Strut Pressure (force) Front Right Hand SidePFL=Strut Pressure (force) Front Left Hand SidePRR=Strut Pressure (force) Rear Right Hand SidePRL=Strut Pressure (force) Rear Left Hand Side

Position and Acceleration Gauges.

The GPS: The speed and location of the truck is monitored by a globalposition system (CPS) receiver. Acceleration is measured by accelerationsensors.

Data Acquisition and Calibration

The data acquisition hardware and data processing for the truck exampleis also analogous to the excavator example.

The data acquisition unit is programmed to take samples up to 1250 timesper second (up to 500 Hz may be useful). Raw data is used by theprocessor to calculate absolute measures of stress and accumulatedfatigue, using a range of calibration constants, some predeterminedbased on the fatigue category detail, dead weight of the system atpredefined by the unloaded stationary state and some updated by regularcalibration as required by the system software. Raw data is kept toinvestigate any incident, bad operating practices or when a failureoccurs. The raw data can be replayed to clearly identify the root causefor incident of extreme high stress or bad practice at any instant.

The actual stress at a measurement location is calculated by multiplyingthe measured strain by Young's modulus for the grade of steel at themeasurement location. A reference value of maximum allowable tensile orcompressive stress (or “strength”) associated with the strain gaugelocation can be calculated, from a stress at which the equipment ispredicted to fail or maximum at which it should operate, either at thestrain gauge location itself or at other non-measured locationspredicted to be most vulnerable based on a FE analysis, multiplied by asafety factor.

The system calculates for data presentation purposes normalizedcompressive and tensile stresses as a ratio or percentage of themeasured stress to the maximum allowable stress taking into account thedead load stress for the particular location at the unloaded stationarylevel position using FEA.

Display of Normalized Measures and Advice

During hauling: The display will alarm if normalized stresses exceed the100% value instantaneous and/or when the cumulative damage for specificdistance traveled exceed threshold limits. The combined effect of haulroad conditions and loading conditions is taken into account.Information can be provided to a 3rd party display system (Modular,Caterpillar, Leica JigJaw) to display this information to the operator.The data can also be transferred to central dispatch with alarm levelsand exact location on the haul road where the alarms occurred. Theamount of recommended speed reduction will depend on the location anddominant operating mode detected—racking, pitching or rolling, by anamount which can be determined by formulae derived from operatingexperience with the truck on the route and/or simulation of the likelyeffect on the stress of reduced speed.

During loading: If the threshold limits exceed the 100% levels due toracking of the chassis due to uneven loading or loading of the truck onuneven ground (one wheel not supported), an alarm is provided to theoperator instantaneously via a 3rd party display so that the operatorcould more truck reduce racking. The cumulative damage is calculated forthe full loading processes i.e. from the time loading starts to the timethe truck starts to drive off.

During Unloading: If the threshold limits exceed the 100% levels duringunloading process, an alarm will be provided to the operatorinstantaneously via a 3rd party display. The sensors (strain gauge) willdetermine whether the high stresses are due to “tail sweeping” (a badpractice where the tray is pulled against the dirt when unloading) andcan alarm the operator via the 3rd party display. The cumulative damageis calculated for the full unloading processes i.e. from the time thestrut starts to lift the tray and until tray rests back on the chassis.

EXAMPLE 3 Electric Rope Shovels

With electric rope shovels, a key goal of the monitoring system istypically to minimize the damage on the boom and dipper handle. Howevermonitoring of the dipper handle is not possible because it slides withinthe boom saddle block. Hence it is extremely difficult to locate sensorson the handles. This difficulty is overcome by locating sensors oncritical locations on the boom to derive the fatigue that the boomexperiences and this can be used from the FEA modelling to infer damageoccurring in the dipper handle. Lateral bending of the dipper handlesduring operations (swing with the dipper engaged in dirt) contributesignificantly to the most common failure mode of the dipper handles.

As with the previous examples on excavators and trucks, the systemapplied to shovels can alarm the operator when the peak stresses/fatiguedamage reaches derived limits for the different conditions the shovelsexperiences during operations.

Recent upgrades introduced to the control system by the OEM do not allowswinging while digging due to concern that it damages the dipper handle.The dipper handle structure can take certain amount of lateral bendingbut would sustain significant damage if design limits are exceeded. TheOEM's approach does not allow any lateral bending which limitperformance of the shovel and would have a major impact on production.

Referring now to FIGS. 7a, 7b, 7c and 8, recommended sensor locations onthe boom of a P&H4100XPB electric shovel are shown, as determined by FEAmodelling. Persons familiar with this model of shovel will understandthe diagrams as they relate to the boom where the dipper handle issupported and slides with other parts of the shovel.

By locating sensors in critical locations 405, 406, 407 & 408, thesystem can provide guidelines to allow for some flexibility to swingwhile digging (creates side loading hence lateral bending of thehandles) but operate within design limits and alarming when peakstresses/fatigue damage exceeds threshold limits of the dipper handle.

The clearances should be set up and maintained to specified values. Byfrequently measuring the clearance between the boom and the dipperhandles and inputting this information, the system to alarming criteriacan be changed to ensure that the handles are operating within designlimits. Detailed FEA has been conducted to develop these relationships.With the critical sensor locations 405, 406, 407 and 408, the system canassist the machine to operate within design limits based on theclearance and alarm threshold set up. The high stresses in the dipperhandle due to lateral bending and torsion and at the torque tubeconnection to the handles can be significant reduced.

Vibrations can occur at start of digging when near to tracks and/or dueto dipper impact on the ground. These can cause significant damage tothe boom and revolving frame structure. Critical sensor location 411 &412 can measure the vibrations that the boom experiences. The system canquantify damage and alarms with specified threshold limits to indicatethese occurrences to the operator and operations.

The sensors 401, 402, 403 and 404 will also monitor the vibrationsduring start of digging due to the dipper impacting the ground in theshipper shaft area.

Boom jacking, using the bucket to jack the machine up, assumes highstress in the boom but has not been quantified. A combination of sensorlocations in the boom can be utilized to monitor and quantify the damageto the boom with alarm threshold limits.

Additional measurements other than strain that may be useful indetermining the operating state include electrical motor outputs for allmotions, operator references, the hoist rope lengths and crowd positionfor electrical shovels

Upgrading of control systems to digital or the used of AC motors withdigital control systems can introduce high vibrations in the entireshovel structure if the setup is not optimized. These have resulted insignificant reduction in rope life and major increase in boom andrevolving frame cracking. Utilizing the above mentioned critical sensorsof the system and electrical outputs, the controls system set upincluding the reference shaping functions (ramps and filtering) for thevarious motions can be optimized to minimize the vibrations that themachine experiences and maximize production.

The system can help the operator change the way one digs to maximizeproductivity while minimizing the fatigue damage to the boom, dipperhandle and revolving frame.

The system can be expanded to monitor critical areas in the revolvingframe and car body of a shovel.

EXAMPLE 4 Drills

Referring to FIG. 9, which shows a part of a Reedrill SKSS drill, abottom part of the mast 510 can be seen at 30° to the verticalorientation. Mast 510 pivots on a fixed support 530 about an axle 520 bythe operation of mast raising cylinders (not shown) attached toattachment points 550 and is lockable into a vertical position or tovarious set angles to the vertical by pins engaging through mast lockingpin insertion plate 540. Critical locations for the strain sensors are501 and 502 on near the axle, 503 and 504 on a mast diagonal (504 is notvisible, disposed on the corresponding side to 503), 505 and 506 on mastmain chords, and 507 and 508 on the fixed support A-frame rear legs.

For drills additional measurement parameters besides strain are pulldown pressures, hoisting/lowering ramp pressures, rotational torques,mast angle and lockout position (whether locking pins are engaged ornot) and pressures to recognise tramming condition.

The primary failure modes for drills are: cracking of the mast mainchord near the hoist cylinder; cracking of the A-frame rear leg; andbreaking of the mast pivot bolts.

A common cause of primary failure modes is the application of the masthoist cylinder force to raise the mast with the mast pin engaged whichcreates very high tensile forces in the above areas. The operator mayalso toggle the hoist to disengage the pin when it is stuck afterdrilling.

The system can alarm when this occurs to prevent the operator doing thisand also estimate the cumulative damage experienced by these components.

In prior art systems there is no indication to the operator that the pinis engaged or not and the cumulative damage caused when the hoist istoggled to release the pins. The system can quantify the cumulativedamage and can trigger inspections of these areas when pre-set thresholdlimits for cumulative damage are exceeded so that cracking of thesecomponents can be detected at early stage to prevent catastrophicfailures.

The cumulative damage while drilling and tramming, etc. can also bequantified but are generally low compared to the causes outlined above.

Advantages of the Invention

As described above, the invention allows for the first time a real-timeassessment of the parameter of most interest to the mine operator—howmuch is the current operation and operator practices damaging theequipment and affecting the productivity and maintenance cost?

In the context of the excavator and truck examples above, the detailedcapabilities enabled are to:

-   -   Minimize stresses/cumulative damage of boom and stick, hence        reduce risk of catastrophic failure(s);    -   Maximize production whilst operating within a safe working        envelope;    -   Provide guidance/assistance to operators through real-time        display in operator cabin;    -   Provide feedback to operations on machine performance;    -   Monitor damage accumulated during operations;    -   Record comprehensive information measured during operations        stored in database for structural integrity management,        maintenance planning and operator training;    -   Give feedback to reduce truck speed based on cumulative damage        the truck sees during hauling due to racking, rolling and        pitching or a combination of these criteria. During loading give        feedback if chassis stress limits exceed due to racking or        during dumping if tail sweeping occurs; and    -   Record up to 500 Hz raw data for detailed incident investigation        and RCA in the event of a failure.

Further advantages specific to electric rope shovels and drills havebeen outlined in the description under Examples 3 and 4 above.

The process of conceiving and experimenting in the course of developinginvention has already resulted in an important insight in relation toexcavators—double benching has been wrongly singled out by manufacturersas the cause of accelerated damage and should not be blamed forequipment failure or be subject to a blanket prohibition. FEA has shownthat although double benching is a high stress operating practice, manyother operating practices, such as below ground digging, can be highlydamaging. The monitoring system of the invention enables rationaloperation of the equipment and real-time feedback on the actual damage,enabling the operator to use the equipment safely in a wide range ofmodes.

Persons skilled in the art will also appreciate that many variations maybe made to the invention without departing from the scope of theinvention.

For example, while the detailed FEA analysis described is needed forbest applying the invention, any workable method of identifying theselocations is within the broadest scope.

Further, while the examples are provided in relation to hydraulicexcavators, trucks, electric rope shovels and drills, other analogousearthmoving equipment can analogously benefit from adaptations of theinvention, including hydraulic shovels, wheel loaders and graders. Itwill be appreciated that while the details may vary, what is central tothe invention is the measurement of actual values of stress and/oraccumulated fatigue enabled by a detailed application of the engineeringparameters and informed choice of strain gauge locations.

In the case of hydraulic shovels in addition to the critical locationsand other parameters (strut pressure and inclinometers forconfiguration) measured in excavators, the bucket release pressures aremeasured. The critical sensor locations are based on similar analysisfor excavators.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but features in variousembodiments of the invention.

It is to be understood that, if any prior art publication is referred toherein, such reference does not constitute an admission that thepublication forms a part of the common general knowledge in the art, inAustralia or any other country.

A predecessor in title to the invention has previously commercialized anearlier variant of the invention on draglines in Australia withoutmaking enabling public disclosures by use or documentary publication.

What is claimed is:
 1. A monitoring system comprising a combination of atruck, gauges, and computing equipment, the monitoring system functionalto calculate, measure and display accumulated damage or closeness tofailure, the truck comprising: a chassis; and the truck suitable forhauling earth on a road, said hauling subjecting the chassis to forcesfrom racking, pitching, rolling, bouncing, loading and unloading; thegauges comprising: a plurality of strain gauges each gauging strain atone of a plurality of strain gauge locations on the chassis, theplurality of strain gauge locations including critical locations atwhich a failure is predicted to occur in one or more of a range ofoperating states of the truck or which are adapted to predict a failurein another location on the chassis; and wheel strut pressure gaugesadapted to gauge whether the truck is racking, pitching or rolling; thecomputing equipment comprising: a data acquisition unit, being acomponent of the computing equipment, the data acquisition unit adaptedto acquire real-time data from the strain gauges and the wheel strutpressure gauges; a processor and non-transitory computer readable memoryadapted to process the acquired real-time data from the strain gaugesand the wheel strut pressure gauges to determine one or more measures ofactual instantaneous stress and a real-time operating state from therange of operating states, and adapted to determine real-timeinformation derived from the real-time operating state; and at least oneoutput device, at least one of which is configured to provideinformation comparing the one or more measures of actual instantaneousstress with corresponding reference values of maximum allowable stress,and to provide the real-time information derived from the real-timeoperating state; and wherein the real-time information derived from thereal-time operating state comprises an amount of cumulative damage orcloseness to failure having regard to the one or more measures of actualinstantaneous stress and the real-time operating state.
 2. Themonitoring system of claim 1, wherein the critical locations include oneor more locations sensitive to failure during racking.
 3. The monitoringsystem of claim 1, wherein the critical locations include one or morelocations sensitive to failure during pitching.
 4. The monitoring systemof claim 1, wherein the critical locations include one or more locationsadapted to identify tail sweeping.
 5. The monitoring system of claim 1,further comprising sensors adapted to measure position and accelerationof the truck.
 6. The monitoring system of claim 1, wherein the one ormore measures of actual instantaneous stress are calculated bymultiplying the real-time data from the strain gauges by a Young'smodulus for a grade of steel at each strain gauge location.
 7. Themonitoring system of claim 6, wherein the processor and non-transitorycomputer readable memory is adapted to calculate a reference value ofmaximum allowable tensile or compressive stress associated with eachstrain gauge location, from a stress at which the failure is predictedor a maximum stress of operation multiplied by a safety factor, and thereal-time information includes a ratio or percentage of the one or moremeasures of actual instantaneous stress compared to the reference value.8. The monitoring system of claim 1, wherein the real-time informationderived from the real-time operating state includes an amount ofrecommended speed reduction during a hauling operation if the amount ofcumulative damage or closeness to failure exceeds threshold limits. 9.The monitoring system of claim 1, wherein the real-time informationderived from the real-time operating state includes a recommendation tomove the truck during a loading operation if the amount of cumulativedamage or closeness to failure exceeds a threshold limit as a result ofracking.
 10. The monitoring system of claim 1, wherein the real-timeinformation derived from the real-time operating state includes arecommendation to correct a tail-sweeping operating state detectedduring an unloading operation.
 11. The monitoring system of claim 1,wherein the output device is adapted to provide the real-timeinformation to an operator of the truck.
 12. The monitoring system ofclaim 1, wherein the output device is adapted to provide the real-timeinformation to a remote monitoring center.